Method and apparatus for reducing the wall thickness of metal tubing



1968 'r. B. ARRINGTON 3,416,346

METHOD AND APPARATUS FOR REDUCING THE WALL THICKNESS OF METAL TUBING Filed May 11, 1964 a K 2 y T W.

FIG 3 INVEI\TOR THOMTAS a. ARRINGTON li 9L ATTORNEY United States Patent 3,416,346 METHOD AND APPARATUS FOR REDUCING THE WALL THICKNESS 0F METAL TUBING Thomas B. Arrington, Detroit, Mich., assigior to Calumet & Hecla, Inc., Allen Park, Mich, a corporation of Michigan Filed May 11, 1964, Ser. No. 366,328 4 Claims. (Cl. 72-189) The present invention relates to method and apparatus for reducing the wall thickness of metal tubing and simultaneously increasing either its outside diameter, its inside diameter, or both.

While the present invention is capable of working with substantially any metal, one field of utility is in producing thin walled metal tubing of metals which are difficult to work, particularly titanium and zirconium.

It is an object of the present invention to provide method and apparatus for reducing the wall thickness of metal tubing while increasing either its inside diameter, its outside diameter, or both, by an operation which comprises applying radial pressure to opposed inner and outer wall surface portions of circumferentially spaced zones of the tubing progressively in the direction of its axis, the pressure exceeding the yield point of the metal so as to produce permanent deformation thereof.

It is a further object of the present invention to provide a method and apparatus as described in the preceding paragraph in which the application of radial pressure applied to opposed inner and outer wall surface portions is applied between a mandrel of increasing diameter in the direction of the progression of the radial pressure and a roll having an arcuate peripheral groove conformed to the mandrel.

It is a further object of the present invention to provide a method and apparatus as described in the foregoing in which radial pressure is applied to the inner and outer surfaces of the tube at two diametrically opposed zones, and in which the material of the tube intermediate the diametrically opposed zones is bulged outwardly to produce an increase in the inside diameter or perimeter of the tubing.

More specifically, it is an object of the present invention to provide method and apparatus for reducing the wall thickness of metal tubing while increasing either its inside diameter, its outside diameter, or both inside and outside diameters, which comprises periodically advancing the tubing longitudinally over a mandrel having a tapered portion of increasing cross-section in the direction of advance of the tubing, applying a rolling pressure between each successive advancing movement of the tubing to the outer surface of the tubing against the mandrel at two diametrically opposed zones of limited circumferential extent so as to reduce the thickness of the tubing and to provide for lateral or circumferential displacement of metal from the zones of pressure application, while simultaneously displacing metal axially so as to produce a thinning of the wall of the tubing at the zones of pressure application as well as an elongation of the tubing.

It is a further object of the present invention to provide method and apparatus as described in the preceding paragraph which includes a circumferential movement of the tube in conjunction with its periodic axial advance.

It is a further object of the present invention to provide apparatus for reducing the wall thickness of metal tubing while at the same time increasing either its inside diameter, its outside diameter, or both, which comprises means for periodically effecting an incremental advance and rotation of a tube, a mandrel over which the tube is advanced and rotated having a tapered portion of increasing diameter in the direction of tube advance, a pair of proposed peripherally grooved rolls engageable with the outside surface of the tube in the zone of the mandrel, the grooves in said rolls including relieved areas to provide for lateral expansion of the tube as a result of reduction in its wall thickness by the rolling operation, means for moving the rolls bodily back and forth parallel to the axis of the tube and mandrel, and means for effecting timed rotation of the rolls so as to approximate rolling contact between the surfaces of the grooves in the rolls and the outside surface of the tube.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing, illustrating a preferred embodiment of the invention, wherein:

FIGURE 1 is a diagrammatic sectional view showing the coaction between a pair of rolls, the mandrel, the tubing, and mechanism for advancing and rotating the tubing.

FIGURE 2 is a sectional view on the line 2-2, FIG- URE 1.

FIGURE 3 is an enlarged sectional view illustrating the relationship between the tubing, mandrel and rolls substantially at the end of a forming stroke.

FIGURE 4 is a diagrammatic view illustrating the mechanism for effecting back and forth traverse of the rolls and timed rotation thereof.

FIGURE 5 is a fragmentry end view of the structure shown in FIGURE 4.

The production of thin walled metal tubing to accurate dimensions both as to inside diameter, outside diameter and uniformity and control of wall thickness presents problems, particularly when the metal employed is difficult to work. The problems are increased where the metals are refractory, or reactive, or both. Titanium and zirconium are examples of such metals. It is impossible as a practical matter to draw tubing of such metals to required relatively small wall thickness where the thin walled tubing is of relatively large diameter.

The present invention of course may be employed with ductile metals such as copper and aluminum, and may also be employed satisfactorily with ferrous metals such for example as stainless steel. However, in the field of difiicult to work and/or reactive metals such as titanium and zirconium, it appears to offer the best if not the only practical method of producing tubing having certain critical relationships as to wall thickness and diameter. In general, the present invention is applicable to the production of tubing of outside diameters between inch and six inches with a wall thickness of .005-.030 inch. Excellent results have been obtained both with copper and titanium in expanding a tube from .625 0D. to .755 OD. while reducing its wall thickness from .045 inch to .024 inch.

The operation is carried out by a method which involves the application of radial pressures progressively in an axial direction to opposed inner and outer zones of the tubing. The presssure applied exceeds the yield point of the metal and produces permanent deformation thereof. Specifically, the metal is displaced from the zone of instantaneous application of pressure both longitudinally or axially of the tube and also transversely or circumferentially thereof. In practice, the pressure is applied to inner and outer zones at one side of the tube and simultaneously to inner and outer zones diametrically opposite to the first zones. As a result of this the transverse or circumferential displacement of metal results in an increase in tube diameter, normally with resulting ovality.

Each cycle of axially progressively applied pressure is preferably applied to two diametrically opposed tube portions and the successive cycle of pressure application is applied to two diametrically opposed tube portions spaced circumferentially from the first two portions as for example by about 30 degrees. In addition, each successive application of axially progressively applied pressure is applied to elongated tube portions successively displaced in an axial direction from the portion of the tube operated on during the preceding cycle. The axial advance between successive cycles is relatively small as for example ,4 of an inch, whereas each cycle of pressure application extends progressively over an elongated portion of the tube, as for example from 12 to 20 inches. By this means a length of tubing is worked on in a series of steps from one end to the other and to the multiplicity of circumferentially spaced zones so that all surface portions of the tube are acted on many times during the complete working cycle.

Conveniently, the foregoing method may be carried out by the apparatus illustrated in the figures. This apparatus comprises a mandrel which is retained by a rod 12 against axial displacement. The mandrel 10 has an intermediate tapered portion 14 of increasing diameter in the direction of tube advance and terminates at the large end in cylindrical portion 40 in which determines the interior diameter of the finished tubing as clearly illustrated in FIGURE 1. If desired, the mandrel 10 may be slightly rotated after each cycle of pressure application.

Associated with the mandrel are a pair of rolls 16- and 18 each having a peripheral groove 20 of generally arcuate cross-section. The rolls 16 and 18 are mounted in a carriage 22 diagrammatically illustrated in FIGURE 4, and means are provided for shifting the carriage rapidly back and forth in a direction parallel to the axis of the mandrel. This means is diagrammatically indicated in FIGURE 4 as crank means comprising a wheel 24 having a link 26 connected eccentrically thereto and connected to the carriage 22. Conveniently, the dimensions of the wheel 24 and link 26 are such that the carriage reciproates rapidly in a rectilinear back and forth stroke of between 12 and 20 inches.

Means are provided for effecting controlled rotation of the rolls 16 and 18 and this means, as diagrammatically illustrated in FIGURES 4 and 5, comprises a gear 28 fixedly connected to one of the rolls, as for example the roll 16, and positioned to roll in mesh with a rack 30. Fixed respectively to the rolls 16 and 18 are gears 32 and 34 which are in mesh with each other so that simultaneously equal but opposite rotation is imparted to the rolls 16 and 18.

It is desired to impart as nearly as possible a true I rolling motion to the metal of the tube during the forward or operating stroke of the apparatus. This stroke is in the direction of the arrow 36 in FIGURE 1. It will of course be appreciated that true rolling motion between the material of either roll and the tube can take place only at one diameter. However, it is not necessary that true rolling motion be present and the dimensions of the gear 28 may be such that true rolling motion takes place between the peripheral outside diameter surfaces of the rolls, these surfaces being indicated at 38 in FIGURE 3. Preferably however, the dimensions of the gear 28 and the location of the rack are such that true rolling motion between each of the rolls 16 and 18 and the material of the tube T takes place at an intermediate diameter.

Referring again to the rolls 16 and 18, it will :be noted that these rolls are mirror images of each other and hence, it will be satisfactory to limit a detailed description to one of the rolls. The roll 16 as seen in FIGURE 1, is provided with recesses 42 and 44 which are designed to occupy positions adjacent the tube T or the mandrel 10 at each end of the stroke of the carriage 22. With either of these clearances adjacent the tube, the tube will be free for movement on the mandrel. Such movement is imparted by a chuck diagrammatically indicated at 46 which is rotatably carried by a head 48 movable axially of the mandrel 10 on a support 50. Suitable means are provided for effecting movement of the head 48 and this means is diagrammatically indicated in FIGURE 1 as comprising a feed screw 52.

The grooves 20 formed in the rolls 16 and 18 are of generally semi-cylindrical but slightly modified crosssection of varying radius in conformity to the taper of the portion 14 of the mandrel. It will be appreciated that by proper design of the shape of the concave groove 20, the wall thickness of the tube T may be reduced to the extent required in conformity with an increase in the diameter of the tube. Similarly, it will be appreciated that as one limiting condition, the use of the grooves 20 of uniform radius will maintain the outside of the tube T constant while the taper in the mandrel will result in an increase in inside tube diameter and a corresponding reduction in wall thickness.

The arrangement described above is illustrated in detail in the enlarged sectional view of FIGURE 3 which may be considered as a section through the axes of the rolls 16 and 18, the tube T, and the mandrel 10'. The mandrel 10 is of true circular cross-section. The grooves 20 of the roll-s 16 and 18 are of arcuate cross-section through a limited angular zone designated 56, the center of curvature being at the axis of the mandrel 10.

Through the angular zones indicated at 60 the surfaces of the generally arcuate grooves 20 are displaced outwardly as indicated at 62, thus providing clearance between the outer surface of the mandrel 10 and the inner surfaces of the generally arcuate grooves of the rolls 16 and 18 to provide for lateral bulging of the tube T, as clearly indicated at 64 in FIGURE 3. This lateral bulging of the tube takes place because the application of opposed radial pressures to the outer and inner surfaces of the tube in the Zones indicated at 56 causes a permanent deformation of the tube and a displacement of metal which takes place both longitudinally or axially of the tube and at the same time, laterally or circumferential ly of the tube. It is this lateral or circumferential displacement of metal, with the resultant bulging of the tube, which permits the present operation in which at least the internal diameter of the tube is increased. With an increase in at least the inside diameter of the tube, there is an increase in the effective circumference of the tube which results in ovality of the tube and a resultant clearance between the internal surface of the tube and the outer surface of the mandrel. This clearance permits the limited axial advance of the tubing following each cycle of pressure application, the forward advance of the tubing, accompanied by limited rotation thereof as previously described, resulting in a change in crosssectional shape of the tubing from a condition of ovality to a condition more nearly approaching a circular shape. Thus, the forward advance of the tubing to the new position as required in the present operation is permitted without binding of the tubing on the mandrel. Since the tubing is relatively thin-walled and may in some cases be reduced to a wall thickness of only a few thousandths of an inch, it will be appreciated that it would be impossible to feed the tube forwardly over a mandrel of increasing cross-section except for the clearance provided as just described.

In accordance with the present operation, the material of the tubing is subjected substantially essentially to compressive forces and these are applied successively over limited areas. In each pressure application cycle, assuming that the areas of pressure application to opposed inner and outer surface portions of the tube are each of approximately 30 degrees extent, it will be apparent that the area throughout which pressure is progressively applied in an axially extending direction may have a width of approximately 3 of the tube circumference and a length equal to the stroke of the machine, which may be between 12 and 20 inches. With this arrangement six cycles of pressure application, each accompanied by a forward advance and limited rotation of the tube, will be required to cause the operation to extend completely around the tube. Assuming an advance of tubing between each cycle of pressure application of A, this will mean that when the tube has been turned through 180 degrees there will be an axial advance of the tubing of approximately 1 /2". Therefore, if the working stroke of the machine is set so that the length of the zone of pressure application is 18" it will be apparent that any particular portion of tube wall will have been subjected to about ten tube expanding and wall thinning operations as it traverses the tapered portion of the mandrel.

The foregoing is merely to clarify the operation and it will of course be apparent that the actual circumferential width of the zone of pressure applications may be changed as required by different materials or by different desired results. Similarly, the amount which the tube is turned and advanced following each rolling cycle may be varied in accordance with the physical properties of the metal of the tubing. Merely by way of example, it is possible to provide a plurality of tube turning steps following rolling cycles without axial advance until the material of the tube has been worked completely around its circumference, after which a limited axial advance may be provided followed by a second succession of tube turning steps without axial advance.

Since the present operation includes rolling the tubing between accurately sized and finished forming rolls in conjunction with a mandrel Whose surface may be accurately finished to required dimensions, it is possible to produce tubing having very desirable properties of interior and exterior surface finish as well as dimensions. Furthermore, since the operation comprises a working of the tube metal by the application of sufiicient pressure to produce permanent deformation, the physical properties of the metal of the finished tube may be particularly desirable for some applications.

While reference has been made to an example in which pressure is applied by each of the rolls over an arc of about 30 degrees of circumference of the tube, the arc may be varied widely, so long as adequate room is left for lateral bulging of tubing consequent to the increase in its inside diameter. This means that where pressure is applied to two diametrically opposite zones, the circumferential arc of each zone must be substantially less than 180 degrees and will normally be less than 90 degrees.

In the operation of the apparatus illustrated the tube may be rotated and/or advanced at each end of the stroke of the carriage 22 if desired. In this way both the forward and return stroke of the carriage 22 constitutes a working stroke. On the other hand, it may be desirable to limit working strokes to those in the direction of feed of the tubing, in which case incremental rotation and/ or advance of the tubing will be limited to the interval when the clearance recesses 44 are adjacent to the tubing.

The drawing and the foregoing specification constitute a description of the improved method and apparatus for reducing the wall thickness of metal tubing in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. Tube expanding and wall thinning apparatus comprising a tapered mandrel of circular cross-section, means for incrementally rotating and advancing tubing over said mandrel in a direction from the small to the large end thereof, a plurality of peripherally grooved rolls engageable with longitudinally elongated circumferentially spaced zones on the exterior of tubing extending over said mandrel, said rolls being shaped to provide clearance laterally of said zones to provide for bulging of the tube laterally intermediate said zones, and means for reciprocating said rolls longitudinally of said mandrel and imparting rotation thereto to approximate rolling contact with tubing on said mandrel.

2. Apparatus as defined in claim 1 in which the grooves in said rolls are dimensioned with respect to the dimensions of said mandrel to roll the tubing so as to decrease wall thickness while increasing at least the inside diameter thereof.

3. Apparatus as defined in claim 1 in which the grooves in said rolls are dimensioned with respect to the dimensions of said mandrel to roll the tubing so as to decrease wall thickness while increasing both the inside and outside diameter thereof.

4. Apparatus as defined in claim 1 in which the means for incrementally advancing the tubing limits the advance to an amount which is permitted by the increase in inside circumference due to the preceding rolling operation without forcing expansion of the tubing by the increasing diameter of the mandrel in the direction of tubing advance.

FOREIGN PATENTS 465,381 5/ 1937 Great Britain. 17,090 1892 Great Britain.

RICHARD J. HERBST, Primary Examiner. H. D. HOINKES, Assistant Examiner.

US. Cl. X.R. 72-208, 370 

1. TUBE EXPANDING AND WALL THINNING APPARATUS COMPRISING A TAPERED MANDREL OF CIRCULAR CROSS-SECTION, MEANS FOR INCREMENTALLY ROTATING AND ADVANCING TUBING OVER SAID MANDREL IN A DIRECTION FROM THE SMALL TO THE LARGE END THEREOF, A PLURALITY OF PERIPHERALLY GROOVED ROLLS ENGAGEABLE WITH LONGITUDINALLY ELONGATED CIRCUMFERENTIALLY SPACED ZONES ON THE EXTERIOR OF TUBING EXTENDING OVER SAID MANDREL, SAID ROLLS BEING SHAPED TO PROVIDE CLEARANCE LATERALLY OF SAID ZONES TO PROVIDE FOR BULGING OF THE TUBE LATERALLY INTERMEDIATE SAID ZONES, AND MEAN FOR RECIPROCATING SAID ROLLS LONGITUDINALLY OF SAID MANDREL AND IMPARTING ROTATION THERETO TO APPROXIMATE ROLLING CONTACT WITH TUBING ON SAID MANDREL. 